The Multiethnic Cohort (MEC) Study was designed to prospectively investigate the relationship of diet and other lifestyle factors to cancer risk in five ethnic groups (African Americans, Japanese Americans, Latinos, Native Hawaiians and Caucasians),and to explore interactions between these risk factors and genetic susceptibility to cancer. Since establishment of the cohort in 1993-96, more than 10 years of follow-up have accrued on the 215,000 participants, bringing the project to a point where its full potential can now be realized. In the current cycle of support, we are re-administering the baseline questionnaire to obtain updated (10-year) dietary and other information on the subjects (e.g., smoking, physical activity, hormonal usage, medications, intercurrent illnesses). We have been analyzing data from the baseline questionnaire, both dietary and non-dietary, as well as data on genetic susceptibility and gene-environment interactions. Altogether, we have published 50 papers from the cohort since early 2003. We have been among the most active participants in NCI's Breast and Prostate Cancer Cohort Consortium, and have shared our data with other members of the consortium, as well as with investigators at outside institutions. For the next 5-year period, we have several dietary scientific aims, including further research into the basis for ethnic differences we observed in diet and cancer relationships, investigation of hypotheses related to dietary constituents recently added to our food composition table (e.g., trans fatty acids, heme iron, glycemic load, heterocyclic amines), study of some less common sites (e.g., non-Hodgkin's lymphoma, ovary and kidney), more in-depth subgroup analyses (e.g., by histology and stage), and investigations of the relationship of diet to cancer survival. We also have several non-dietary scientific aims, particularly related to investigating as- yet unexplainable ethnic differences in breast and lung cancer risk. The important work necessary to maintain the cohort and its several databases will continue, including administration of another short follow- up questionnaire and regular enhancements to the unique food composition table. Finally, we will continue to train graduate students and postdoctoral fellows. We expect this research not only to expand knowledge of the role of environmental risk factors and genes in cancer risk, but also to further an understanding of the basis for ethnic/racial disparities in cancer occurrence and survival.